Past apparatuses attempting to produce an automatic sizing function for lapping machines were deficient in that they required constant monitoring and frequent replacement of cooperating components.
For example prior devices provided for stationary probes extending in an upward direction with the sensing tip of the probe periodically contacted by an actuating arm which in turn was physically attached to the rotating upper plate. This arrangement required a fixed attachment of the actuating member to the plate, with such attachment requiring extreme tolerances such that the fixed member be assembled and permanently maintained in parallelism to the lapping surface. As the sensing tip of the probe was successively struck by the rotating independent actuating arm, it became worn and/or deformed such that it did not function accurately. As the sensing probe was in direct displacement with respect to the fixed actuating aem such probe would be rendered inoperative when and if the lap was lowered beyond its normal operating plane i.e. a plane determined by the presence of a workpiece superimposed between the upper and lower lapping surfaces.
The present invention overcomes these deficiencies by providing a ring-like actuating member which has continuous rolling contact with a probe actuating lever. By this arrangement the probe is disposed in a downwardly directed probing direction with the actuating lever being restricted in its degree of rotation about its pivot point irregardless of the displacement of the lapping surface such that the probe cannot be damaged or rendered ineffectual regardless of the extreme positioning of the upper lap plate.